[Insight-users] MetaImage 'Offset' (vs 'Position') tag

[Frederic Perez]

Hello Jim,

thank you very much for the information!

Best regards,

Frederic Perez

 --- "Miller, James V (Research)" <millerjv at crd.ge.com> escribió: 
> The MetaIO library in Insight/Utilities/MetaIO is what ITK
> uses to write Meta images.  I consider this the "master" 
> implementation of the Meta format. 
> 
> Looking through that code, it looks like Offset and Position
> are synonymous.  Calling SetPosition/GetPosition actually 
> modifies the Offset fields. 
> 
> When finally writing the Meta image, only "Offset" is written.
> 
> I think vtkMetaImageReader should read the Offset field.
> vtkMetaImageReader also does not handle some of the mechanisms
> that MetaIO allows for specifying files (ElementDataFile tag
> with patterns).
> 
> Jim
> 
> 
> -----Original Message-----
> From: Frederic Perez [mailto:fredericpcx at yahoo.es]
> Sent: Thursday, November 04, 2004 9:15 AM
> To: insight-users at itk.org; vtkusers at vtk.org
> Subject: [Insight-users] MetaImage 'Offset' (vs 'Position') tag
> 
> 
> 
> Hello insight-users,
> 
> I've been succesfully generating and using MetaImage files
> in Insight. At present I am also reading MetaImage files 
> using VTK 4.4, with the aid of the vtkMetaImageReader 
> class created by Andy Cedilnik (thank you very much).
> 
> I have noticed that the origin of the input image (more
> concretely, the origin of the related vtkImageData) is 
> set to (0, 0, 0) although the Insight generated files 
> specify the origin to be, for example, 
> "Offset = -176.5 5.01561 -1539.5" (in the header file).
> This is also the case when reading the Insight generated 
> MetaImage files into ParaView. This is annoying for example
> when reading two files corresponding to the right and 
> left lungs---they clash even though their respective 
> origins differ.
> 
> After learning a bit about the MetaImage format
> http://caddlab.rad.unc.edu/software/MetaIO/MetaIO-Introduction.htm
> and browsing the VTK's vtkMetaImageReader.cxx source file
> I have found that Insight uses the tag "Offset" while
> VTK uses the tag "Position" to specify the origin of the 
> volume data. Substituting "Offset" by "Position" seems 
> to fix the problem, both for the vtkMetaImageReader and
> for ParaView. One can edit the header files manually or
> execute a perl command to get the substitution done, for
> example. However, maybe it would be better to do the 
> changes in the Insight code itself since the tag "Offset" 
> does not seem to exist (am I wrong?) in 
> http://caddlab.rad.unc.edu/software/MetaIO/MetaIO-Introduction.htm
> (maybe that page is not updated?!)
> 
> Hope this helps,
> 
> Frederic Perez
> 
> 
> 
> 		
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